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bcache: ignore read-ahead request failure on backing device 

When md raid device (e.g. raid456) is used as backing device, read-ahead
requests on a degrading and recovering md raid device might be failured
immediately by md raid code, but indeed this md raid array can still be
read or write for normal I/O requests. Therefore such failed read-ahead
request are not real hardware failure. Further more, after degrading and
recovering accomplished, read-ahead requests will be handled by md raid
array again.

For such condition, I/O failures of read-ahead requests don't indicate
real health status (because normal I/O still be served), they should not
be counted into I/O error counter dc->io_errors.

Since there is no simple way to detect whether the backing divice is a
md raid device, this patch simply ignores I/O failures for read-ahead
bios on backing device, to avoid bogus backing device failure on a
degrading md raid array.

Suggested-and-tested-by: Thorsten Knabe <linux@thorsten-knabe.de>
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Coly Li 2019-06-28 19:59:29 +08:00 committed by Jens Axboe
parent e6dcbd3e6c
commit 578df99b1b
1 changed files with 12 additions and 0 deletions
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12
drivers/md/bcache/io.c
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@ -58,6 +58,18 @@ void bch_count_backing_io_errors(struct cached_dev *dc, struct bio *bio)
WARN_ONCE(!dc, "NULL pointer of struct cached_dev");
/*
* Read-ahead requests on a degrading and recovering md raid
* (e.g. raid6) device might be failured immediately by md
* raid code, which is not a real hardware media failure. So
* we shouldn't count failed REQ_RAHEAD bio to dc->io_errors.
*/
if (bio->bi_opf & REQ_RAHEAD) {
pr_warn_ratelimited("%s: Read-ahead I/O failed on backing device, ignore",
dc->backing_dev_name);
return;
}
errors = atomic_add_return(1, &dc->io_errors);
if (errors < dc->error_limit)
pr_err("%s: IO error on backing device, unrecoverable",